Characterisation of Blast Loading Parameters from Cuboidal Explosive Charges in the Far Field

The detonation of a high explosive results in a release of energy, as a charge undergoes a rapid change in state when it converts from solid to a mass of high pressure, high temperature gas. This gas expands, compressing the surrounding air, forming a shockwave. Shockwaves can cause serious damage to infrastructure and human health, challenging the blast engineer to accurately quantify and predict blast loading. Semi-empirical methods are favoured as they decrease the financial, time or computing expense necessitated by experimental tests or numerical modelling.

This thesis presents in-depth experimental and numerical quantification of blast wave behaviour from cuboidal charges in the far field (Z≥2m/kg1/3). The free edge of a cuboidal charge is not equidistant from the point of detonation, as is the case for a spherical charge. Cuboidal charges, therefore, display significantly different behaviour than spherical charges. Experimental data and numerical modelling shows cuboidal charges exhibit distinct shape effects: a significant subsequent shock following the primary shock, varying with scaled distance and charge rotation. The additional shock outweighs the primary shock in some instances, particularly in the mid to late far field region. Numerical modelling indicates that this feature is a result of complex early-stage loading not present in commensurate hemispherical charges.

Current semi-empirical methods are unsuitable for predicting the behaviour of cuboidal charges due to the presence of shape effects not seen in spherical charges- which many semi-empirical blast load predictors are designed for. Data presented in this thesis is used to synthesize a new model for cuboidal charge load prediction, wherein both primary and subsequent shocks are approximated as time-adjusted hemispherical charges. This predictor is presented as an empirical method for characterizing cuboidal charge behaviour in the far field, which can be used to expand the functionality of existing semi-empirical blast models.